Adjustable backrests capable of providing support for the lower back of a vehicle driver or passenger are known. Such backrests may provide lordosis support and can be adjustable through the use of a cable and may employ a foamed material as a cushioning element and can be adjusted to conform to the contours of the spine.
The known mechanism does not permit any accommodation to the changed or changing spinal column curvature. For example in our long automobile travel, the spinal column curvature alters greatly because of the holding work which necessarily is exerted by the outstretched arms of the driver holding the steering wheel because the total weight of the upper portion of the body under these conditions must be supported in a disadvantageous manner. This muscle and holding work, for supporting the body under conditions of insufficient or improper support, is transmitted fully to the musculature and skeletal system and results in considerable exhaustion and muscle stress. The muscles which are brought into play for this work require up to 40 times as much blood and expend up to 40 times the energy of an upper body with proper anatomical support whose muscles are not subjected to holding work.
The lordosis support must thus be able to adjust well to every spinal column shape and, upon applying full pressure to the back of the user in its adjusted form, should not autogenously alter to ensure that each individual vertebra is fully supported regardless of the curvature.
German patent document DE-OS 34 40 846 discloses, for example, an automobile seat whose backrest comprises a frame and a plate received in the frame. The plate is provided with vertically-extending longitudinal slits in which a lumbar-support device is movable. The lumbar support can be adjusted via a hand wheel through a shaft articulated on the frame to vary its stiffness and to move vertically.
The lumbar support is directly connected with the frame. As a consequence, all vibrations of the vehicle imparted by the road are fully transmitted to the back of the operator.